A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter. Analog multimeters are sometimes referred to as "volt-ohm-meters", abbreviated VOM. Digital multimeters are usually referred to as "digital-multi-meters", abbreviated DMM. A multimeter can be a handheld device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. Such an instrument will commonly be found in a calibration lab and can be used to characterize resistance and voltage standards or adjust and verify the performance of multi-function calibrators.